1. Field of the Invention
The field of this invention comprises composite pigments and their manufacture and, more particularly, composite pigments containing zinc oxide.
2. Description of the Prior Art
The most pertinent prior art known to the Applicant is U.S. Pat. No. 3,028,250 to Dunn. It is distinguished in Examples 3 and 9 to 13. U.S. Pat. No. 3,004,857 to Merson and Dunn is also very pertinent, but only because it contains the same teachings of the above-mentioned Dunn patent and as such is also distinguished in the Examples.
U.S. Pat. Nos. 2,956,861; 2,898,191 and 1,944,158 are pertinent in that they disclose the preparation of zinc oxide from carbonates. None disclose or suggest, however, the composite pigment of the present invention.
U.S. Pat. No. 2,210,087 is pertinent in that it disclosed a method for making manganese activated zinc orthosilicate which included the steps of precipitating zinc carbonate and manganese carbonate on finely divided particles of silica and calcining the products in the temperature range of 900.degree. C. to 1400.degree. C. With the present invention orthosilicates are avoided since they inhibit the pigment's photoconductive properties.
Belgian Pat. No. 629,390 disclosed a composite pigment comprising zinc oxide deposited on a core of silica produced by melting and vaporizing zinc or zinc-bearing ore and depositing the resulting zinc oxide on finely divided particles of silica. Patentee does not disclose nor suggest, however, that the composite pigment is of photoconductive quality.
U.S. Pat. No. 3,674,476 disclosed a process for producing photoconductive zinc oxide powder by heating zinc hydroxide or basic zinc carbonate at a minimum temperature of 180.degree. C. in the presence of water and under an elevated pressure of at least 1.2 atmospheres, but does not disclose nor suggest depositing zinc oxide on an inert core material.
U.S. Pat. Nos. 3,897,248; 3,802,880; 3,197,307; 3,155,504 and 3,060,134 are cited as background information regarding photoconductive pigments. None disclose nor suggest, however, the present invention.
U.S. Pat. No. 2,139,995 discloses a zinc compound precipitated on blanc fixe to form a composite pigment used in rubber compounding. It is not relevant to the present invention in that it specifies uncalcined zinc carbonate-hydroxide on the blanc fixe and indicates calcined compounds not effective. Barium sulfate appears to be an anomolous inert.
Japanese Pat. No. 130893/1974 is pertinent in that it discloses depositing basic zinc carbonate on the surface of solid particles. The resulting composite particle is said to have utility in the compounding of rubber. Patentee neither discloses nor suggests the subject invention, however. This is particularly evident in that it specifies a decomposition temperature below 600.degree. C. stating that the coating is zinc hydroxide basic zinc carbonate or a mixture of them and is also non-crystalline. It is also stated to be non-photoconductive. Only where reaction between the zinc compound and a reactive core occurs does the surface area of the composite pigment exceed 5.8 square meters/gram.
U.S. Pat. Nos. 2,958,578; 2,325,737 and 1,999,573 are cited as background information regarding compounding zinc with rubber. None discloses nor suggest, however, the present invention.